This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-194473, filed Jul. 8, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a gas spring apparatus adapted for use as means for applying tension to a tension wire, such as a trolley wire, aerial electric power line, etc.
FIGS. 4A, 4B and 4C are schematic views individually showing conventional gas spring apparatuses. In any of these prior art examples, a reaction force increases as a rod 1 is caused to get into a cylinder 2 by means of an external force F so that a high-pressure gas in a gas chamber 3 is compressed. These prior art apparatuses are of the compression spring type. In these examples, the rod 1 becomes stationary with respect to the cylinder 2 when the external force F balances with the reaction force that is generated by the pressure in the gas chamber 3.
In general, gases are lower in molecular weight and viscosity than liquids, so that it is harder to seal a gas than to seal a liquid. It is more difficult, in particular, to seal a sliding portion of the rod 1 that is in sliding contact with the cylinder 2.
In a structure designed so that the gas charged in the gas chamber 3 is sealed by means of a sealing portion 5, as shown in FIG. 4A, gas leakage occurs in an early stage in a sliding portion between the rod 1 and the sealing portion 5. Thus, prolonged use of this type is not easy.
Accordingly, the sealing effect of the sealing portion 5 may be improved by sealing a liquid in a liquid chamber 6 that is provided on the side of the sealing portion 5 of the rod 1, as shown in FIG. 4B or 4C. In the example shown in FIG. 4B, the liquid chamber 6 and the gas chamber 3 are divided by means of a free piston 7 that is inserted in the cylinder 2. Since the liquid in the liquid chamber 6 is sealed by means of the sealing portion 5, the sliding portion of the rod 1 can be sealed with ease. In the case of the prior art example shown in FIG. 4C, the same purpose is attained by using an elastic element 8 such as a metallic bellows that is held in the cylinder 2.
Thus, the compression spring type is a dominant type for the conventional gas spring apparatuses. In order to use the compression spring type as a tension spring for a balancer of a trolley wire, for example, however, a load in the direction of pull must be converted into a load in the direction of compression by means of a pull mechanism, an additional measure.
As a known example of the tension spring type, a tension regulating apparatus is described in Jpn. Pat. Appln. KOKOKU Publication No. 6-62070. In this prior art apparatus, the rod side of the internal space of a cylinder is defined as an oil chamber, the opposite side is left open to the atmosphere, and a balancer (accumulator) is separately attached to the oil chamber by means of piping. In this case, the gas pressure in the accumulator is equal to the pressure in the oil chamber. The tension increases as this pressure acts on a plunger so that the rod is pulled externally. Thus, the apparatus has a structure of the tension spring type.
However, the structure of the tension spring type involves the following problems.
(1) Since the accumulator having a high-pressure gas sealed therein is required besides the cylinder, the projected area of the apparatus is wider, so that installation requires a wider space. Further, the gross weight of the apparatus is heavier by a margin corresponding to the weight of the accumulator.
(2) Since the gas in the accumulator is sealed by means of an elastic rubber bag or free piston, aging of rubber causes gas leakage, resulting in lowering of performance. It is difficult, therefore, to use the apparatus maintenance-free for a long period of time.
(3) Since the atmosphere side of the cylinder is in contact with the open air, rusting is liable to occur.
A tensioning apparatus of the gas spring type is described in Jpn. Pat. Appln. KOKAI Publication No. 6-16068. Since this tensioning apparatus is of the compression spring type, however, it inevitably becomes complicated in construction, bulky, and heavy if it is designed to be of the tension spring type, thus leaving room for improvement.
Accordingly, the object of the present invention is to provide a high-durability gas spring apparatus of tension-type, which can be designed to be compact and lightweight and can be used without suffering gas leakage for a long period of time.
In order to achieve the above object, a gas spring apparatus according to the present invention comprises an outer tube, a cylinder held in the outer tube and having a proximal end portion fixed to the outer tube and a closed distal end face, a rod inserted into the outer tube through a hole in an end wall of the outer tube and having a distal end portion projecting inside the cylinder and a proximal end portion projecting outside the outer tube, a sealing portion provided on that part which is penetrated by the rod of the outer tube, a piston provided on the distal end portion of the rod and dividing the interior of the cylinder between a first liquid chamber situated on the side of the sealing portion and a low-pressure gas chamber situated on the side remoter from the sealing portion, and a partition member dividing the interior of the outer tube between a high-pressure gas chamber and a second liquid chamber. The first liquid chamber in the cylinder and the second liquid chamber in the outer tube are internally connected, and a gas is charged in the high-pressure gas chamber at a higher pressure than in the low-pressure gas chamber.
In the gas spring apparatus of the invention constructed manner, the pressure in the high-pressure gas chamber causes the liquids in the liquid chambers to generate a force that pulls the rod into the cylinder. When a force that pulls out the rod from the cylinder acts on the rod, the liquid in the first liquid chamber moves toward the second liquid chamber, and the capacity of the high-pressure gas chamber is reduced by a margin corresponding to the volume of the moved portion of the liquid, so that the pressure increases. If the pressure in the high-pressure gas chamber increases, liquid pressures in the liquid chambers also increase, so that a reaction force that acts on the rod is enhanced. Based on the operation described above, this gas spring apparatus can function as a tension-type gas spring apparatus.
According to the present invention, there may be provided a tension-type gas spring apparatus in which a load in the direction of pull can be applied directly to the rod. Since the high-pressure gas chamber and the liquid chambers are arranged in the outer tube, moreover, the apparatus can be made compact and lightweight. Since the sealing portion of this gas spring apparatus seals the liquids, sealing is easy, and the sealing effect can be enhanced. Since the low-pressure gas chamber in the cylinder is closed, furthermore, the problem of rusting in the cylinder can be solved.
Preferably, the partition member of the invention is formed of a metal bellows that can extend and contract in the axial direction of the outer tube. According to this invention, a high-pressure gas can be hermetically sealed by means of the outer tube, metal bellows, etc., and the apparatus can be used maintenance-free without suffering gas leakage for a long period of time.
According to the present invention, moreover, the outer tube and the rod may be connected to a tension line, such as a trolley wire or aerial electric power line, and a tension line supporting member, respectively, or to the supporting member and the tension line, respectively. In this case, the tension line is subjected to a force such that the rod is pulled into the cylinder by means of the pressure in the high-pressure gas chamber. According to this invention, there may be provided a tension-type gas spring apparatus capable of applying an appropriate tension to a tension line such as a trolley wire as well as enjoying the aforementioned effects.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.